High energy radiation detection technology commonly employs scintillation crystals as a detection material which is capable to block radiation effectively and produce light by absorbing the energy of the radiation, then uses a high gain photomultiplier device to generate electrical pulse signals by photoelectrically converting and amplifying the weak optical signals, and obtains information about energy, time, spatial position, etc. of the high energy radiation by analyzing the pulse signals. This kind of solid-state detector is commonly called a scintillation detector.
When high energy radiation is incident into scintillation crystals, usually photoelectric effect, Compton scattering effect and electron pair effect in different proportions will occur according to the value of the radiation energy, and the radiation energy will therefore be finally entirely absorbed by the scintillation crystals, being accompanied with the release of an extremely weak scintillation light. For the scintillation light in visible or ultraviolet region, all the information of the high energy radiation can be acquired by detecting the photoelectrically converted scintillation light through high-sensitivity signal amplification devices (such as photomultiplier tubes, PMT). For example, the intensity of the output pulse signals of the photomultiplier tubes indicates the energy of the high energy radiation; the occurrence time of the pulse signals indicates the incident time of the high energy radiation; the intensity distribution of the pulse signals in a plurality of photomultiplier tubes indicates the incident position of the high energy radiation. Because of their advantages of high detection efficiency, large signal-to-noise ratio, rapid response, etc., conventional scintillation detectors are widely used in the researches of nuclear medicine, security check, high energy physics and cosmic rays detection, and have become a main means of the current radiation detection technology that is indispensable.
Conventional scintillation detectors have relatively simple structures. Especially, when they are used for detecting and positioning, conventional scintillation detectors usually rely on a structure of a plurality of identical photomultiplier tubes coupled with a scintillation crystal array to determine the incident position of high energy radiation. However, in this structure, there are large blind areas in the gaps between the photomultiplier tubes, leading to a non-uniform distribution of detection efficiency in the entire imaging system of the detector and a low spatial resolution. Therefore, great emphasis is attached to how to improve detection efficiency, imaging uniformity and spatial resolution in radiation detection and imaging technology.
FIG. 1 shows the basic structure of a conventional scintillation detector generally comprising a scintillation crystal array module 1 coupled with 4 photomultiplier tubes (PMTs) 2 having an identical size and shape. FIG. 2 is the top view of the above conventional scintillation detector. As shown in FIG. 2, the scintillation crystal array module 1 covers the surface of the detection windows A, B, C, and D of the 4 PMTs 2. The scintillation crystal array is generally formed of scintillation crystal material rods bonded together with a reflective film. The scintillation crystal array module 1 and the PMT detection windows A, B, C, and D can be either bonded to each other by using a high-transparency optical adhesive, or indirectly coupled with each other by interposing a photoconductive material (such as organic plastics, glass, optical fibers, etc.) between the scintillation crystals and PMTs.
When high energy radiation is incident into the scintillation crystal array, each high energy radiation will excite a single scintillation crystal at the incident position, and enable the scintillation crystal to produce scintillation light by photoelectric effect or Compton scattering effect. According to the characteristics of different scintillation crystal materials, the number of scintillation photons generated is usually in the magnitude of 103˜104, and the corresponding scintillation light has a wavelength of 200 nm˜600 nm (in the ranges of ultraviolet or visible light). Due to the reflection effect of the reflective material at the surface of a single scintillation crystal, the scintillation light will be constrained in the single scintillation crystal and be reflected multiple times, and finally transmit from one end of the scintillation crystal into the PMT at the other end of the scintillation crystal. In the case that there is no reflective material coated on the surface of the single scintillation crystal, the scintillation light pass through the scintillation crystal, enter an adjacent scintillation crystal unit and transmit continuously. In the end, the scintillation light will be collected at the incident glass port of the PMT, and pulse signals will be produced. Therefore, the intensity distribution of the pulse signals in the PMTs indicates the incident position of the high energy radiation; the total intensity of the pulse signals is proportional to the incident energy of the high energy radiation; the occurrence time of the pulse signals is related to the incidence time of the high energy radiation; and the spatial positioning accuracy of the detector is determined by the cross sectional dimension of the single scintillation crystal.
For the conventional scintillation detector, a positioning calculation method, commonly known as Anger logical positioning method, can be used to estimate the interacting position of incident high energy radiation based on ratios of different intensities of output pulse signals generated by the 4 PMTs excited by the identical incident high energy radiation. By respectively indicating the intensities of the voltage signals generated by the 4 PMTs by VA, VB, VC and VD, the spatial positions X and Y, as well as energy E of the high energy radiation can be expressed respectively as:
      X    =                            V          B                +                  V          D                                      V          A                +                  V          B                +                  V          C                +                  V          D                          Y    =                            V          A                +                  V          B                                      V          A                +                  V          B                +                  V          C                +                  V          D                          E    =                  V        A            +              V        B            +              V        C            +              V        D            